CN113789460B - Si-containing lead-free low-temperature solder alloy and preparation process thereof - Google Patents

Si-containing lead-free low-temperature solder alloy and preparation process thereof Download PDF

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CN113789460B
CN113789460B CN202110913289.6A CN202110913289A CN113789460B CN 113789460 B CN113789460 B CN 113789460B CN 202110913289 A CN202110913289 A CN 202110913289A CN 113789460 B CN113789460 B CN 113789460B
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solder alloy
alloy
solder
quartz tube
smelting
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CN113789460A (en
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刘亚
陈�胜
吴长军
王建华
苏旭平
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Changzhou University
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C13/00—Alloys based on tin
    • C22C13/02—Alloys based on tin with antimony or bismuth as the next major constituent
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/26—Selection of soldering or welding materials proper with the principal constituent melting at less than 400 degrees C
    • B23K35/262—Sn as the principal constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/02—Making non-ferrous alloys by melting
    • C22C1/03—Making non-ferrous alloys by melting using master alloys
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

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Abstract

The invention relates to a lead-free low-temperature solder alloy containing Si and a method for preparing the sameThe solder alloy consists of 35 to 47 weight percent of Bi, 1 weight percent of Ag, 0.5 weight percent of Si and the balance of Sn; the preparation steps are as follows: weighing corresponding particle raw materials according to the weight percentage, firstly smelting Ag-Si intermediate alloy by using a tungsten-electrode consumable magnetic control arc furnace, then putting the intermediate alloy into a box-type resistance furnace for annealing, and then smelting the solder alloy. The invention improves the mechanical property and the wettability of the traditional Sn-Bi-Ag series solder alloy by adding trace Si element, has no obvious influence on the melting point, and can inhibit the intermetallic compound layer (Cu) of the interface reaction between the solder alloy and Cu6Sn5) The aging service strength of the photovoltaic solder strip coating is improved; the method not only solves the problems of burning loss and oxidation of the alloy elements caused by different melting points of the alloy elements, but also enables the hard and brittle phases (Bi) in the alloy to be more dispersed and fine, obtains better structure and effectively improves the performance of the solder alloy.

Description

Si-containing lead-free low-temperature solder alloy and preparation process thereof
Technical Field
The invention relates to the technical field of photovoltaic welding strip welding materials, in particular to a Si-containing lead-free low-temperature solder alloy suitable for a photovoltaic welding strip coating and a preparation process thereof.
Background
The photovoltaic solder strip is used as a junction part in the solar cell and plays a very important role in the development of the solar cell. For a long time, Sn-Pb eutectic solder is always the first choice of coating solder for photovoltaic solder strips by virtue of the advantages of excellent wettability, stable solderability, low price, rich reserves and the like. The Sn-Pb eutectic solder contains 40 wt% of Pb and has a melting point of about 181 ℃. However, as environmental awareness increases, it is becoming increasingly recognized that the toxicity of Pb and its compounds is not negligible to the human and natural hazards. Furthermore, the photovoltaic module is also miniaturized and lightened, and the thinner the cell is, the lower the welding temperature of the solder strip is. Therefore, the development of lead-free low-temperature solder-strip-coated solders is a necessary trend in photovoltaic solder strip development.
At present, extensive research on lead-free low-temperature solder with solder strip coating has been conducted, and by replacing Pb in Sn-Pb alloy with another component, the research systems are as follows: Sn-Ag based, Sn-Cu based, Sn-Ag-Cu based, Sn-Zn based, and Sn-Bi based. The melting point of the Sn-Bi lead-free solder is 138 to 232 ℃; and the melting temperature is obviously reduced along with the increase of the Bi content, so that the melting point of the solder can be adjusted by adjusting the Bi content. The low melting point makes the solder strip have advantages in the development trend of low temperature soldering of photovoltaic solder strips, and becomes a typical representative of lead-free low-temperature photovoltaic solder strip coating solders. However, the existing Sn-Bi solder has a bad influence on the mechanical properties of the solder alloy because the Bi-rich phase is easy to segregate and coarsen crystal grains, and the wettability of the Sn-58Bi solder alloy is far lower than that of the traditional Sn-40Pb solder. Therefore, further improvements in the mechanical properties and wetting properties of Sn — Bi solder alloys are desired.
Application number 201810194058.2 discloses a low melting point Sn-Bi-Al series lead-free solder alloy material and a preparation method thereof, wherein the alloy comprises the following components in percentage by weight: 15-25%; al: 0.5-2%; the balance being Sn. According to the method, the planetary ball mill is used for preparing the solder alloy, so that Al particles are uniformly distributed in the solder and the alloy, the technical problem that Al and Sn-Bi alloy are not easy to mutually melt is solved, the mechanical property of the solder is improved, and the wettability of the solder on a Cu substrate is not researched; it is known that addition of an appropriate amount of Ag improves the mechanical properties and wettability of Sn-Bi solder, but there are few studies on Sn-Bi-Ag based solder alloys. Application No. 201811390305.2 discloses a Sn-Bi system low-silver lead-free solder alloy in which Bi: 40 percent; ag: 0.5 percent; cu is more than or equal to 0.5 percent and less than or equal to 1.5 percent; sn is the balance, Cu element is added on the basis of Sn-40Bi-0.5Ag alloy, the mechanical property and wettability of the solder are improved, but the improvement effect is still limited compared with the traditional Sn-40Pb solder alloy, and the cost is increased due to the addition of Cu, so that the industrial production is limited.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: in order to overcome the defects in the prior art, the invention provides the lead-free low-temperature solder alloy containing Si and the preparation process thereof, so as to better improve the tensile strength of the solder alloy and greatly improve the wettability of the solder alloy.
The technical scheme adopted by the invention for solving the technical problems is as follows: the lead-free low-temperature solder alloy containing Si comprises the following raw material components in percentage by weight: bi: 35% -47%, Ag: 1%, Si: 0.5% and the balance Sn.
Furthermore, the purities of the raw materials Bi, Ag, Si and Sn are all more than or equal to 99.99%.
A preparation process of the Si-containing lead-free low-temperature solder alloy comprises the following steps:
s1, weighing raw materials, and respectively weighing Sn particles, Bi particles, Ag particles and Si sheets in corresponding amounts according to the weight percentage of each raw material component;
s2, uniformly mixing the Ag particles weighed in the step S1 with the Si sheets, putting the mixture into a tungsten-electrode consumable-free magnetic control electric arc furnace, vacuumizing the electric arc furnace, wherein the vacuum degree is 3 multiplied by 10-3～6×10-3Pa; filling argon with the purity of 99.99 percent and the pressure of one standard atmospheric pressure, vacuumizing, repeating for 2-5 times, smelting under the protection of the argon, wherein the smelting voltage is 220V, the smelting current is 10-50A, the electric arc is closed after the smelting time is kept for 30-60 s, liquid alloy is obtained, cooling is carried out for 5-30 s, then smelting is carried out, repeating for 3 times, and then cooling is carried out, so that the Ag-Si intermediate alloy is obtained;
s3, putting the Ag-Si intermediate alloy in the step S2 into a quartz tube, vacuumizing and sealing, and then putting the quartz tube into a box-type resistance furnace at 1000 ℃ for annealing for 7 days;
s4, respectively filling the Sn particles and the Bi particles weighed in the step S1 and the Ag-Si intermediate alloy annealed in the step S3 into a quartz tube, and then vacuumizing and sealing the quartz tube;
s5, putting the quartz tube filled with the raw materials in the step S4 into a pit furnace for smelting, wherein the temperature of the pit furnace is set to be 400 ℃, the quartz tube is kept warm for 12 hours after the temperature in the pit furnace reaches the set temperature, and the quartz tube is vertically inverted and shaken every 30 minutes during the process so as to ensure that the components in the smelting process are uniform;
s6, taking out the solder alloy melted in the step S5 by using crucible tongs, and then quickly putting the solder alloy into a cold water bucket for cooling;
s7, cutting the solder alloy cooled in the step S6 into pieces by using vanadium steel locking pliers, and then putting the pieces into a new quartz tube to repeat the steps S5 and S6 for three times;
and S8, completely cooling to obtain the Sn-Bi-Ag-Si solder alloy.
The invention has the beneficial effects that: on the basis of the known Sn-Bi-Ag solder alloy, the invention forms a new Sn-Bi-Ag-Si solder alloy by adding trace Si element, further improves the mechanical property and the wettability of the lead-free solder alloy by adding trace non-metallic element (semiconductor material) Si, and has no obvious influence on the melting point; during preparation, the Ag-Si intermediate alloy is smelted by a tungsten-electrode consumable magnetic control arc furnace, and then the solder alloy is smelted, so that the problem that alloy elements are not easy to add (the melting points of tin and bismuth are lower, the melting points of silver and silicon are higher, burning loss and oxidation of the alloy elements are easy to cause) is solved, the hard and brittle phase Bi phase in the alloy is dispersed and fine, a better structure is obtained, and the performance of the solder alloy is effectively improved.
Drawings
The invention is further illustrated with reference to the following figures and examples.
FIG. 1 is a structural diagram of a Sn-Bi-Ag based solder alloy of a comparative example.
FIG. 2 is a structural diagram of the Sn-Bi-Ag-Si based solder alloy of the present invention.
FIG. 3 is a graph showing the tensile strength of the Sn-Bi-Ag-Si based solder alloy of the present invention compared with that of the comparative example Sn-Bi-Ag based solder alloy.
FIG. 4 is a graph showing a comparison of contact angle curves of the Sn-Bi-Ag-Si based solder alloy of the present invention and the Sn-Bi-Ag based solder alloy of the comparative example.
FIG. 5 is a graph showing a comparison between the melting point of the Sn-Bi-Ag-Si based solder alloy of the present invention and the melting point of the Sn-Bi-Ag based solder alloy of the comparative example.
Detailed Description
The solder composition formulations of the specific examples of the present invention and the comparative examples are shown in table 1:
TABLE 1
Figure BDA0003204469640000041
The specific preparation methods of the above examples and comparative examples are as follows:
example 1:
(1) firstly, Ag particles and Si sheets in the example 1 in the table 1 are weighed according to the weight percentage and mixed, then the mixture is put into a tungsten-electrode consumable-free magnetic control electric arc furnace, the electric arc furnace is vacuumized, and the vacuum degree is 6 multiplied by 10-3Pa; filling argon, wherein the argon is high-purity argon with the purity of 99.99 percent, the pressure is one standard atmospheric pressure, vacuumizing, repeating for 5 times, smelting under the protection of the argon, the smelting voltage is 220V, the smelting current is 50A, keeping for 30-60 s, then closing an electric arc to obtain liquid alloy, cooling for 30s, then smelting, repeating for 3 times, and cooling to obtain the Ag-Si alloy;
(2) filling the Ag-Si alloy in the step (1) into a quartz tube, vacuumizing and sealing, and then putting into a box-type resistance furnace at 1000 ℃ for annealing for 7 days;
(3) weighing Sn particles and Bi particles described in the embodiment 1 in the table 1 according to the weight percentage, putting the Sn particles and the Bi particles and the Ag-Si intermediate alloy prepared in the step (2) into a quartz tube, and vacuumizing and sealing the quartz tube;
(4) and putting the quartz tube filled with the raw materials into a well type furnace for smelting. The temperature of the furnace is set to be 400 ℃, the furnace is kept warm for 12 hours after reaching the set temperature, and the quartz tube is inverted and shaken up and down every 30 minutes to ensure that the components are uniform in the melting process;
(5) taking out the solder alloy melted in the step (4) by using crucible tongs, and then quickly putting the solder alloy into a cold water bucket for cooling;
(6) and (3) shearing the solder alloy cooled in the step (5) by using vanadium steel locking pliers, then putting the solder alloy into a new quartz tube, vacuumizing and sealing the quartz tube, and repeating the steps (4) and (5) for three times. Finally taking out the alloy and water quenching the alloy to obtain Sn-35Bi-1Ag-0.5Si solder alloy;
(7) and after metallographic treatment, the prepared Sn-35Bi-1Ag-0.5Si solder alloy is analyzed for microstructure morphology by a scanning electron microscope, and mechanical property test, wetting property test and melting point test are carried out.
Example 2:
(1) ag particles and S described in example 2 of Table 1 were mixedWeighing the i sheets according to the weight percentage, mixing, putting the mixture into a copper crucible of a non-consumable electric arc furnace, vacuumizing the electric arc furnace, wherein the vacuum degree is 6 multiplied by 10-3Pa; filling argon, wherein the argon is high-purity argon with the purity of 99.99 percent, the pressure is one standard atmospheric pressure, vacuumizing, repeating for 5 times, smelting under the protection of the argon, the smelting voltage is 220V, the smelting current is 50A, keeping for 60s, then closing an electric arc to obtain liquid alloy, cooling for 30s, then smelting, repeating for 3 times, and cooling to obtain the Ag-Si intermediate alloy;
(2) filling the Ag-Si alloy in the step (1) into a quartz tube, vacuumizing and sealing, and then putting into a box-type resistance furnace at 1000 ℃ for annealing for 7 days;
(3) weighing Sn particles and Bi particles described in the embodiment 2 in the table 1 according to the weight percentage, putting the Sn particles and the Bi particles and the Ag-Si intermediate alloy prepared in the step (2) into a quartz tube, and vacuumizing and sealing the quartz tube;
(4) and putting the quartz tube filled with the raw materials into a well type furnace for smelting. The temperature of the furnace is set to be 400 ℃, the temperature is kept for 12 hours after the furnace reaches the set temperature, and the quartz tube is inverted and shaken up and down every 30 minutes during the process so as to ensure the components in the melting process to be uniform;
(5) taking out the solder alloy melted in the step (4) by using crucible tongs, and then quickly putting the solder alloy into a cold water bucket for cooling;
(6) and (3) shearing the solder alloy cooled in the step (5) by using vanadium steel locking pliers, then putting the solder alloy into a new quartz tube, vacuumizing and sealing the quartz tube, and repeating the steps (4) and (5) for three times. Finally taking out the alloy and water quenching the alloy to obtain Sn-37Bi-1Ag-0.5Si solder alloy;
(7) and after metallographic treatment, the prepared Sn-37Bi-1Ag-0.5Si solder alloy is analyzed for microstructure morphology by a scanning electron microscope, and mechanical property test, wetting property test and melting point test are carried out.
Example 3:
(1) firstly, the Ag particles and the Si sheets in the example 3 in the table 1 are weighed and mixed according to the weight percentage, then the mixture is put into a copper crucible of a non-consumable electric arc furnace, the electric arc furnace is vacuumized, and the vacuum degree is 6 multiplied by 10-3Pa; filling argon gas with 99.99% of high-purity argon gas and pressure of onePerforming standard atmospheric pressure, vacuumizing again, repeating for 5 times, finally smelting under the protection of argon, wherein the smelting voltage is 220V, the smelting current is 50A, keeping for 60s, closing an electric arc to obtain liquid alloy, cooling for 30s, then smelting again, repeating for 3 times, and cooling to obtain an Ag-Si intermediate alloy;
(2) filling the Ag-Si intermediate alloy in the step (1) into a quartz tube, vacuumizing and sealing, and putting the quartz tube into a box-type resistance furnace at 1000 ℃ for annealing for 7 days;
(3) weighing Sn particles and Bi particles in the embodiment 3 in the table 1 according to the weight percentage, putting the Sn particles and the Bi particles and the Ag-Si intermediate alloy prepared in the step (2) into a quartz tube, and vacuumizing and sealing the quartz tube;
(4) and putting the quartz tube filled with the raw materials into a well type furnace for smelting. The temperature of the furnace is set to be 400 ℃, the furnace is kept warm for 12 hours after reaching the set temperature, and the quartz tube is inverted and shaken up and down every 30 minutes to ensure that the components are uniform in the melting process;
(5) taking out the solder alloy melted in the step (4) by using crucible tongs, and then quickly putting the solder alloy into a cold water bucket for cooling;
(6) cutting the solder alloy cooled in the step (5) into pieces by using vanadium steel locking pliers, placing the cut solder alloy into a new quartz tube, vacuumizing and sealing the quartz tube, repeating the steps (4) and (5) for three times, and finally taking out the quartz tube and performing water quenching to obtain Sn-35Bi-1Ag-0.5Si solder alloy;
(7) and after metallographic treatment, the prepared Sn-45Bi-1Ag-0.5Si solder alloy is analyzed for microstructure morphology by a scanning electron microscope, and mechanical property test, wetting property test and melting point test are carried out.
Example 4:
(1) firstly, the Ag particles and the Si sheets in the example 4 of the table 1 are weighed and mixed according to the weight percentage, then the mixture is put into a copper crucible of a non-consumable electric arc furnace, the electric arc furnace is vacuumized, and the vacuum degree is 6 multiplied by 10-3Pa; filling argon gas with the pressure of one standard atmosphere and the purity of 99.99 percent of argon gas, vacuumizing again, repeating for 5 times, smelting under the protection of argon gas, the smelting voltage is 220V, the smelting current is 50A, closing electric arc after keeping for 60s to obtain liquid alloy, cooling for 30s, and then carrying out arc weldingIt is smelted, repeated for 3 times, and cooled to obtain the Ag-Si intermediate alloy.
(2) Filling the Ag-Si intermediate alloy in the step (1) into a quartz tube, vacuumizing and sealing, and then putting into a box-type resistance furnace at 1000 ℃ for annealing for 7 days;
(3) weighing Sn particles and Bi particles described in the embodiment 4 in the table 1 according to the weight percentage, putting the Sn particles and the Bi particles and the Ag-Si intermediate alloy prepared in the step (2) into a quartz tube, and vacuumizing and sealing the quartz tube;
(4) and putting the quartz tube filled with the raw materials into a well type furnace for smelting. The temperature of the furnace is set to be 400 ℃, the furnace is kept warm for 12 hours after reaching the set temperature, and the quartz tube is inverted and shaken up and down every 30 minutes to ensure that the components are uniform in the melting process;
(5) taking out the solder alloy melted in the step (4) by using crucible tongs, and then quickly putting the solder alloy into a cold water bucket for cooling;
(6) cutting the solder alloy cooled in the step (5) into pieces by using vanadium steel locking pliers, placing the cut solder alloy into a new quartz tube, vacuumizing and sealing the quartz tube, repeating the steps (4) and (5) for three times, and finally taking out the quartz tube and performing water quenching to obtain Sn-35Bi-1Ag-0.5Si solder alloy;
(7) and after metallographic treatment, the prepared Sn-47Bi-1Ag-0.5Si solder alloy is analyzed for microstructure morphology by a scanning electron microscope, and mechanical property test, wetting property test and melting point test are carried out.
Comparative example 1:
(1) the Sn particles, Bi particles and Ag particles described in comparative example 1 in Table 1 were weighed and mixed in percentage by weight, and then the mixture was put into a quartz tube and sealed by vacuum pumping.
(2) And putting the quartz tube filled with the raw materials into a well type furnace for smelting. When the alloy is smelted, the temperature of the furnace is set to be 300 ℃, the furnace is kept warm for 12 hours after reaching the set temperature, and the quartz tube is inverted and shaken up and down every 30 minutes to ensure that the components are uniform in the melting process;
(3) taking out the solder alloy melted in the step (2) by using crucible tongs, and then quickly putting the solder alloy into a cold water bucket for cooling;
(4) cutting the solder alloy cooled in the step (3) into pieces by using vanadium steel locking pliers, putting the cut solder alloy into a new quartz tube, repeating the steps (2) and (3) for three times, and finally taking out the cut solder alloy and water quenching the cut solder alloy to obtain Sn-35Bi-1Ag solder alloy;
(5) and after metallographic treatment, the prepared Sn-35Bi-1Ag solder alloy is analyzed for microstructure morphology by using a scanning electron microscope, and mechanical property test, wetting property test and melting point test are carried out.
Comparative example 2:
(1) weighing and mixing Sn particles, Bi particles and Ag particles in comparative example 2 in the table 1 according to weight percentage, and then filling the mixture into a quartz tube for vacuumizing and sealing;
(2) and putting the quartz tube filled with the raw materials into a well type furnace for smelting. When the alloy is smelted, the temperature of the furnace is set to be 300 ℃, the furnace is kept warm for 12 hours after reaching the set temperature, and the quartz tube is inverted and shaken up and down every 30 minutes to ensure that the components are uniform in the melting process;
(3) taking out the solder alloy melted in the step (2) by using crucible tongs, and then quickly putting the solder alloy into a cold water bucket for cooling;
(4) cutting the solder alloy cooled in the step (3) into pieces by using vanadium steel locking pliers, putting the cut solder alloy into a new quartz tube, repeating the steps (2) and (3) for three times, and finally taking out the cut solder alloy for water quenching to obtain Sn-37Bi-1Ag solder alloy;
(5) and after metallographic treatment, analyzing the microstructure morphology by using a scanning electron microscope, and carrying out mechanical property test, wettability test and melting point test on the prepared Sn-37Bi-1Ag solder alloy.
Comparative example 3:
(1) weighing and mixing Sn particles, Bi particles and Ag particles described in comparative example 3 in the table 1 according to weight percentage, then filling the mixture into a quartz tube, vacuumizing and sealing the quartz tube;
(2) and putting the quartz tube filled with the raw materials into a shaft furnace for smelting. When the alloy is smelted, the temperature of the furnace is set to be 300 ℃, the furnace is kept warm for 12 hours after reaching the set temperature, and the quartz tube is inverted and shaken up and down every 30 minutes to ensure that the components are uniform in the melting process;
(3) taking out the solder alloy melted in the step (2) by using crucible tongs, and then quickly putting the solder alloy into a cold water bucket for cooling;
(4) shearing the solder alloy cooled in the step (3) by using vanadium steel locking pliers, putting the solder alloy into a new quartz tube, repeating the steps (2) and (3) for three times, and taking out the solder alloy for water quenching to obtain Sn-45Bi-1Ag solder alloy;
(5) the prepared Sn-45Bi-1Ag solder alloy is subjected to metallographic treatment, and then the microstructure morphology is analyzed by a scanning electron microscope, and the mechanical property test, the wetting property test and the melting point test are carried out.
Comparative example 4:
(1) weighing and mixing Sn particles, Bi particles and Ag particles described in comparative example 4 in the table 1 according to weight percentage, then filling the mixture into a quartz tube, vacuumizing and sealing the quartz tube;
(2) and putting the quartz tube filled with the raw materials into a well type furnace for smelting. When the alloy is smelted, the temperature of the furnace is set to be 300 ℃, the furnace is kept warm for 12 hours after reaching the set temperature, and the quartz tube is inverted and shaken up and down every 30 minutes to ensure that the components are uniform in the melting process; .
(3) Taking out the solder alloy melted in the step (2) by using crucible tongs, and then quickly putting the solder alloy into a cold water bucket for cooling;
(4) cutting the solder alloy cooled in the step (3) into pieces by using vanadium steel locking pliers, putting the cut solder alloy into a new quartz tube, repeating the steps (2) and (3) for three times, and finally taking out the cut solder alloy for water quenching to obtain Sn-47Bi-1Ag-0.5Si solder alloy;
(5) and after metallographic treatment, the prepared Sn-47Bi-1Ag solder alloy is analyzed for microstructure morphology by using a scanning electron microscope, and mechanical property test, wetting property test and melting point test are carried out.
Sample detection:
(1) the Sn-Bi-Ag solder alloys obtained in comparative examples 1 to 4 and the Sn-Bi-Ag-Si solder alloys obtained in examples 1 to 4 were examined to obtain a texture profile comparison chart, as shown in FIGS. 1 and 2. The a, b, c, d graphs in FIG. 1 are texture maps of Sn-35Bi-1Ag, Sn-37Bi-1Ag, Sn-45Bi-1Ag and Sn-47Bi-1Ag solder alloys, respectively, while the a, b, c, d graphs in FIG. 2 are texture maps of Sn-35Bi-1Ag-0.5Si, Sn-37Bi-1Ag-0.5Si, Sn-45Bi-1Ag-0.5Si and Sn-47Bi-1Ag-0.5Si solder alloys, respectively. As can be seen from FIG. 1, the gray color with the lower contrastThe base phase is (Sn), the phase with higher contrast is (Bi), and a small amount of Ag is added3The Sn phase is dispersed and distributed on the (Sn) matrix. As the Bi content increases, the irregular (Bi) size becomes relatively larger and the segregation becomes more pronounced. Comparing the a diagram in fig. 1 and 2, the b diagram in fig. 1 and 2, the c diagram in fig. 1 and 2, the d diagram in fig. 1 and 2, respectively, it can be seen that after a trace amount of Si is added to the Sn-Bi-Ag solder alloy, (Bi) is uniformly distributed in the solder structure in a discontinuous phase, and is more dispersed and finer, effectively suppressing the formation and segregation of coarse brittleness (Bi).
(2) The Sn-Bi-Ag solder alloys obtained in comparative examples 1 to 4 and the Sn-Bi-Ag-Si solder alloys obtained in examples 1 to 4 were prepared into I-shaped tensile specimens, the widths and thicknesses of the tensile specimens were measured with a vernier caliper, and the specimens were respectively stretched with a universal electronic tester WDT-3030KN to calculate the tensile strength of the solder alloys.
FIG. 3 is a graph comparing the tensile strength of the solder alloys of examples 1-4 with the tensile strength of the solder alloys of comparative examples 1-4. It can be seen that the solder alloys obtained in comparative examples 1 to 4 and examples 1 to 4 all exhibited a tendency that the tensile strength decreased with the increase in the Bi content. However, the Sn-Bi-Ag-Si solder alloys obtained in examples 1 to 4 all had better tensile strength than the Sn-Bi-Ag solder alloy of the comparative example, which shows that the solder alloy for solder ribbon coating had significantly improved tensile strength after adding a small amount of Si. The tensile strengths of the solder alloys of examples 1 to 4 were 86.74MPa, 84.67MPa, 80.95MPa, and 77.21MPa, respectively; the tensile strengths of the solder alloys of comparative examples 1 to 4 were 83.376MPa, 77.73MPa, 73.2MPa, and 65.47MPa, respectively.
(3) 0.15 to 0.25g of each of the Sn-Bi-Ag solder alloys obtained in comparative examples 1 to 4 and the Sn-Bi-Ag-Si solder alloys obtained in examples 1 to 4 was weighed, and the weighed weights were recorded in order, followed by a wettability test using a high-temperature wetting angle measuring apparatus, and the heating temperatures were all 170 ℃. The whole dripping process is recorded by a CCD high-speed camera, after the experiment is finished, a picture is captured from a video recorded by the camera, the ADSA software is used for vectorizing the alloy liquid image so as to extract contour data, and finally the SESDROPD software is used for fitting, calculating and analyzing the data so as to obtain a contact angle. In the test, the wetting property of the solder alloy is judged by adopting the contact angle of the alloy liquid when the alloy liquid drops on the Cu plate for 5s, and the smaller the contact angle is, the better the wettability of the alloy is.
FIG. 4 is a graph comparing the contact angle curves of the solder alloys of examples 1-4 with those of comparative examples 1-4. Comparing the contact angles of example 1 with comparative example 1, example 2 with comparative example 2, example 3 with comparative example 3, and example 4 with comparative example 4, respectively, it can be seen that the magnitude of the contact angle of the Sn-Bi-Ag-Si solder alloy obtained in examples 1 to 4 is significantly smaller than that of the solder alloy in comparative examples 1 to 4, indicating that the wettability of the Sn-Bi-Ag-Si solder alloy in the examples is significantly better than that of the Sn-Bi-Ag solder alloy in the comparative examples. The contact angles of the solder alloys of examples 1 to 4 were 54.49 °, 41.13 °, 31.36 °, and 30.36 ° respectively; the solder alloy contact angles of comparative examples 1 to 4 were 106.22 °, 88.46 °, 70.65 °, and 62.596 °, respectively.
(4) 20 to 50mg of each of the Sn-Bi-Ag solder alloys obtained in comparative examples 1 to 4 and the Sn-Bi-Ag-Si solder alloys obtained in examples 1 to 4 was weighed, the weighed weights were sequentially recorded, and then a melting point test was performed using a differential scanning calorimeter (DSC 404F3A00) at a temperature increase rate of 5 ℃/Min.
FIG. 5 is a graph comparing the melting points of the solder alloys of examples 1-4 with the melting points of the solder alloys of comparative examples 1-4. Comparing the melting points of example 1 and comparative example 1, example 2 and comparative example 2, example 3 and comparative example 3, and example 4 and comparative example 4, respectively, it was found that the melting points of the Sn-Bi-Ag-Si solder alloys obtained in examples 1 to 4 were not much different from those of the solder alloys in comparative examples 1 to 4. The difference between the melting points of the example 4 and the comparative example 4 is the largest and is only 2.2 ℃, and the difference between the melting points of the example 1 and the comparative example 1 is the smallest 0.6 ℃. In actual production, the method cannot cause substantial change due to factors such as errors. The melting points of the solder alloys of examples 1 to 4 were 163.5 ℃, 161.6 ℃, 144.2 ℃ and 142.8 ℃, respectively; the melting points of the solder alloys of comparative examples 1 to 4 were 164.1 deg.C, 162.4 deg.C, 142.2 deg.C, and 140.6 deg.C, respectively.
In light of the foregoing description of the preferred embodiment of the present invention, many modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims (6)

1. A lead-free low-temperature solder alloy containing Si is characterized in that: the solder alloy comprises the following raw material components in percentage by weight: bi: 35% -47%, Ag: 1%, Si: 0.5 percent, and the balance of Sn; the preparation process of the Si-containing lead-free low-temperature solder alloy comprises the following steps:
s1, weighing raw materials, and respectively weighing Sn particles, Bi particles, Ag particles and Si sheets in corresponding amounts according to the weight percentage of each raw material component;
s2, uniformly mixing the Ag particles weighed in the step S1 with the Si sheets, putting the mixture into a tungsten-electrode consumable-free magnetic control electric arc furnace, vacuumizing the electric arc furnace, wherein the vacuum degree is 3 multiplied by 10-3～6×10-3Pa; filling argon with the purity of 99.99 percent and the pressure of one standard atmospheric pressure, vacuumizing, repeating for 2-5 times, smelting under the protection of the argon, wherein the smelting voltage is 220V, the smelting current is 10-50A, the electric arc is closed after the smelting time is kept for 30-60 s, liquid alloy is obtained, cooling is carried out for 5-30 s, then smelting is carried out, repeating for 3 times, and then cooling is carried out, so that the Ag-Si intermediate alloy is obtained;
s3, placing the Ag-Si intermediate alloy in the step S2 into a quartz tube, vacuumizing, sealing, and then placing into a box-type resistance furnace at 1000 ℃ for annealing for 7 days;
s4, respectively filling the Sn particles and the Bi particles weighed in the step S1 and the Ag-Si intermediate alloy annealed in the step S3 into a quartz tube, and then vacuumizing and sealing the quartz tube;
s5, putting the quartz tube filled with the raw materials in the step S4 into a pit furnace for smelting, wherein the temperature of the pit furnace is set to be 400 ℃, the quartz tube is kept warm for 12 hours after the temperature in the pit furnace reaches the set temperature, and the quartz tube is vertically inverted and shaken every 30 minutes during the process so as to ensure that the components in the smelting process are uniform;
s6, taking out the solder alloy melted in the step S5 by crucible tongs, and quickly putting the solder alloy into a cold water bucket for cooling;
s7, cutting the solder alloy cooled in the step S6 into pieces by using vanadium steel locking pliers, and then putting the pieces into a new quartz tube to repeat the steps S5 and S6 for three times;
and S8, completely cooling to obtain the Sn-Bi-Ag-Si solder alloy.
2. The Si-containing lead-free low temperature solder alloy of claim 1, wherein: the solder alloy comprises the following raw materials in percentage by weight: bi: 35% and Ag: 1%, Si: 0.5% and the balance Sn.
3. The Si-containing lead-free low temperature solder alloy of claim 1, wherein: the solder alloy comprises the following raw materials in percentage by weight: bi: 37%, Ag: 1%, Si: 0.5% and the balance Sn.
4. The Si-containing lead-free low temperature solder alloy of claim 1, wherein: the solder alloy comprises the following raw materials in percentage by weight: bi: 45%, Ag: 1%, Si: 0.5% and the balance Sn.
5. The Si-containing lead-free low temperature solder alloy of claim 1, wherein: the solder alloy comprises the following raw materials in percentage by weight: bi: 47%, Ag: 1%, Si: 0.5% and the balance Sn.
6. The Si-containing lead-free low temperature solder alloy of claim 1, wherein: the purities of the raw materials Bi, Ag, Si and Sn are more than or equal to 99.99 percent.
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